Solar tracker, and method for operating same

ABSTRACT

The present invention relates to a solar tracker and to a method for operating same, capable of controlling the azimuth and elevation in accordance with the changing portion of the sun in the celestial sphere by the diurnal motion and annual motion so as to enable solar energy collection apparatuses to track the travel of the sun for a long period of time. The solar tracker according to the present invention is provided with two rotating shafts which are responsible for the right ascension and declination, respectively, wherein the movements of the rotating shafts are not independent from each other. One rotating shaft moves in dependence on the other rotating shaft, wherein the dependent relationship is mechanically constrained according to the correlation between the diurnal motion and annual motion of the sun. As a result, the tracker of the present invention can track the diurnal motion of the sun with a single actuator and, at the same time, compensate the annual motion which changes in the meridian altitude according to the change of seasons. The solar tracker and the method for operating same in accordance with the present invention, enables the tracking of the diurnal motion and annual motion of the sun using one actuator, thereby maximizing solar power generation efficiency and reducing initial installation costs and maintenance costs.

TECHNICAL FIELD

The present invention relates to a solar tracker, and more particularly,to a solar tracker and a method of operating the solar tracker that mayadjust an azimuth and an altitude based on a change in a position of theSun by a diurnal motion and an annual motion, in order for a solarenergy collector to track a path of the Sun moving on the celestialsphere for a long period of time.

BACKGROUND ART

A solar tracker is designed to adjust each rotation shaft of a mechanismto adjust an azimuth and an altitude for a light collector to bepositioned perpendicularly to the Sun and maintain an optimalefficiency. Based on a degree of freedom (DOF) of the mechanism, thesolar tracker may be classified into a 1-DOF solar tracker and a 2-DOFsolar tracker. In general, a DOF of a mechanism is identical to thenumber of rotation shafts used for a solar tracker and thus, the 1-DOFand the 2-DOF solar tracker may be simply referred to as a 1-shaftsystem and a 2-shaft system instead of using the technical term “DOF.”

In a conventional solar tracker according to conventional technology,the 1-shaft system may track the Sun on a daily basis while rotatingfrom east to west preferentially based on a diurnal motion of the Sun,and manually correct a meridian altitude of the Sun that changesannually. However, such a manually correcting method may beinconvenient. In addition, although the manually correcting method isquarterly performed, for example, four times a year, a maximum value ofa potential tracking error may reach approximately 23.5° whichcorresponds to the Earth's rotational axial tilt. In terms of trackingthe diurnal motion of the Sun, a maximum error angle that may occur dueto an annual motion of the Sun may be greater than an error that mayoccur when the solar tracker fails to track the Sun for approximatelyone and a half hours, 90 minutes, in tracking the diurnal motion of theSun on a daily basis while rotating from east to west.

The 2-shaft system may considerably reduce an error of the solar trackerby automatically adjusting a change in a meridian altitude occurring dueto the annual motion of the Sun in addition to the diurnal motion of theSun. However, an additional actuator and controller may be used andthus, initial equipment costs may increase, and power consumption andmaintenance costs of the added actuator and controller may be required.Thus, the solar tracker may be utilized advantageously in economicalterms only when a gain earned from improved generation efficiencygreatly exceeds the added costs. However, in actuality, implementing the2-shaft system which is economically advantageous and, at the same time,performs a reliable operation may not be readily achieved due to addedinitial costs and maintenance costs for frequent breakdowns.

DISCLOSURE OF INVENTION Technical Goals

An aspect of the present invention provides a solar tracker and a methodof operating the solar tracker to solve such issues described in theforegoing. The solar tracker is provided with two rotation shafts whichare responsible for a right ascension and a declination, respectively,and do not operate independently from each other. For example, onerotation shaft may be mechanically dependent on the other rotationshaft. The two rotation shafts may have a dependent relationship andmove in accordance with a correlation between a diurnal motion and anannual motion of the Sun. Thus, the solar tracker may track the diurnalmotion of the Sun through a single actuator and also automaticallycorrect the annual motion in which a meridian altitude changes dependingon a solar term.

Technical Solutions

According to an aspect of the present invention, there is provided asolar tracker including a right ascension rotation shaft installed inparallel with the Earth's rotation axis and configured to track a changein a right ascension occurring due to a diurnal motion of the Sun, aright ascension rotation actuator configured to actuate the rightascension rotation shaft, a declination rotation shaft perpendicular tothe right ascension rotation shaft and configured to correct a change ina declination occurring due to an annual motion of the Sun, and adeclination actuation mechanism configured to transfer a portion ofdriving power of the right ascension rotation actuator to thedeclination rotation shaft to allow the declination rotation shaft toreciprocatingly rotate upwards and downwards.

The declination actuation mechanism may include additional components tobe described hereinafter to enhance efficiencies.

The declination actuation mechanism may include a one-way clutchinstalled at a point in a power transfer path from the right ascensionrotation actuator to the declination rotation shaft, and configured toselectively transfer, to the declination rotation shaft, only an amountof rotation used for the right ascension rotation shaft to track thediurnal motion of the Sun in the daytime by transferring a one-wayrotation component of the driving power generated from the rightascension rotation actuator.

The declination actuation mechanism may include a reduction ratioadjuster installed at one point in the power transfer path from theright ascension rotation actuator to the declination rotation shaft, andconfigured to adjust a cycle of one reciprocating up and down rotationalmotion of the declination rotation shaft and to precisely match thecycle of the reciprocating up and down rotational motion of thedeclination rotation shaft to a cycle of tracking approximately 365times of the diurnal motion by the right ascension rotation shaft.

The declination actuation mechanism may include a coupling installed atone point in the power transfer path from the right ascension rotationactuator to the declination rotation shaft, and configured toselectively connect or block a dependent relationship between the rightascension rotation shaft and the declination rotation shaft and toindependently adjust the declination rotation shaft without affectingthe right ascension rotation shaft.

The declination actuation mechanism may be designed to allow thedeclination rotation shaft to reciprocatingly rotate with a displacementof the Earth's rotational axial tilt while the right ascension rotationshaft tracks the diurnal motion approximately 365 times, based on acorrelation between the diurnal motion and the annual motion of the Sun.For the designing, the declination actuation mechanism may include adeclination reducer configured to receive a portion of the driving powerof the right ascension rotation actuator, convert a rotation ratio, andoutput the converted rotation ratio, a crank attached to an output shaftof the declination reducer, a rocker fixed to the declination rotationshaft and reciprocatingly rotating upwards and downwards at the Earth'srotational axial tilt based on the change in the declination occurringdue to the annual motion of the Sun, and a connecting rod connecting oneend of the crank to one end of the rocker to form a four-bar linkage andconfigured to convert a rotational motion of the crank to thereciprocating up and down rotational motion of the rocker.

In designing the declination actuation mechanism using the four-barlinkage, the crank, the rocker, or the connecting rod may include anadjuster configured to adjust a location of a joint or a link length tochange a motional displacement and a sectional speed of thereciprocating up and down rotational motion of the declination rotationshaft.

Further, to verify whether the solar tracker tracks the annual motion,the solar tracker may include a declination display device configured toconvert an amount of rotation of the declination rotation shaft to anangle and display the angle, or a solar term display device configuredto convert the amount of rotation to a solar term of a year and displaythe solar term.

Effects of Invention

According to example embodiments, a solar tracker disclosed herein maysimultaneously track a diurnal motion and an annual motion of the Sunthrough a single actuator and thereby, maximizing solar power generationefficiency while reducing initial installation costs and maintenancecosts.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a solar tracker according to anembodiment of the present invention.

FIG. 2 illustrates a diurnal motion of the Sun in the spring equinoxwhich is observed at a point in the northern hemisphere.

FIG. 3 illustrates a change in a meridian altitude of the Sun in thespring equinox based on an observation point in the northern hemisphere.

FIG. 4 illustrates a change in a meridian altitude and in a diurnalmotion of the Sun based on a season which is observed at a point in thenorthern hemisphere.

FIG. 5 illustrates a change in a meridian altitude based on a latitudeand a season.

FIG. 6 illustrates a declination of the Sun that changes along theecliptic in an equatorial coordinate system, and an operation principleof a solar tracker according to an embodiment of the present invention.

FIG. 7 illustrates an example of a support and a pillar capable ofadjusting an altitude and an azimuth of a right ascension rotation shaftaccording to an embodiment of the present invention.

FIG. 8 illustrates an example of designing a frame of a solar tracker,and 2-degrees of freedom (DOF) equivalent apparatus according to anembodiment of the present invention.

FIG. 9 illustrates an example of utilization of a balance weight toequally allocate a load to rotation shafts of a solar tracker accordingto an embodiment of the present invention.

FIG. 10 illustrates an example of designing a right ascension rotationactuator of a solar tracker according to an embodiment of the presentinvention.

FIG. 11 illustrates an example of designing a declination actuationmechanism of a solar tracker according to an embodiment of the presentinvention.

FIG. 12 illustrates an example of a change in an angle of a lightcollector holder by a declination actuation mechanism of a solar trackerbased on a solar term according to an embodiment of the presentinvention.

FIG. 13 illustrates an example of including a coupling, a one-wayclutch, or a reduction ratio adjuster in a declination actuationmechanism according to an embodiment of the present invention.

FIG. 14 illustrates an example of a diurnal operation and a nocturnaloperation of a solar tracker based on a solar term according to anembodiment of the present invention.

FIG. 15 illustrates an example of including a solar term display device,or a declination display device or a right ascension display device in asolar tracker according to an embodiment of the present invention.

FIG. 16 is a flowchart illustrating an example four-step method ofoperating a solar tracker according to an embodiment of the presentinvention.

FIG. 17 is a flowchart illustrating an example seven-step method ofoperating a solar tracker according to an embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT INVENTION

Before describing fundamental examples and various modified examples ofa solar tracker 1000 disclosed herein, a correlation between a diurnalmotion and an annual motion of the Sun a01 will be described first.Reference numerals used throughout are defined as follows.

1000: Solar tracker 100: Right ascension rotation shaft

200: Right ascension rotation actuator 210: Actuator

220: Right ascension reducer 300: Declination rotation shaft

400: Declination actuation mechanism 410: Declination reducer

420: Reciprocating rotation conversion mechanism 421: Crank

422: Rocker 423: Connecting rod

424: Joint location and link length adjuster 430: Coupling

440: Reduction ratio adjuster 450: One-way clutch

460: Declination display device 470: Solar term display device

480: Right ascension display device 500: Frame

510: Support 520: Pillar

530: Right ascension rotation support 540: Declination rotation support

550: Light collector holder 560: Balance weight

600: Light collector

a01: Sun a02: Earth

a03: Sunlight a04: Diurnal motion path of the Sun

a05: Earth's rotational axial tilt (approximately 23.5°)

a10: Equatorial coordinate system

a11: Right ascension a12: Declination

a13: Celestial axis a15: North celestial pole

a16: South celestial pole a17: Equatorial plane

a18: Ecliptic a19: Celestial sphere

a20: Horizontal coordinate system a21: Azimuth

a22: Altitude a23: Meridian altitude

a24: Meridian a25: South point

a26: North point a27: East point

a28: West point a29: Horizontal plane

a30: Earth coordinate system a31: Longitude

a32: Latitude a33: Colatitude

a34: Earth's rotation axis a35: North Pole

a36: South Pole a37: Equator

a40: Solar term a41: Spring equinox (solar term)

a42: Summer solstice (solar term) a43: Autumn equinox (solar term)

a44: Winter solstice (solar term)

a45: Spring equinoctial point (position on the celestial sphere)

a46: Summer solstice point (position on the celestial sphere)

a47: Autumn equinoctial point (position on the celestial sphere)

a48: Winter solstice point (position on the celestial sphere)

a51: Earth's rotation a52: Earth's revolution

a53: Annual motion of the Sun a54: Diurnal motion of the celestialsphere

a55: Rotational motion of a right ascension rotation shaft to track adiurnal motion

a56: Reciprocating rotational motion of a declination rotation shaft tocompensate for an annual motion

L0: Base link L1: First link

L2: Second link J1: First joint

J2: Second joint

A change in an azimuth a21 and an altitude a22 of the Sun a01 to beobserved along a horizontal coordinate system a20 results from rotationand revolution of the Earth a02. As illustrated in FIG. 2, in a diurnalmotion of the Sun 01 on the celestial sphere which is observed from ahorizontal plane a29, when the Earth a02 makes one rotation for a day,an azimuth a21 of the Sun a01 changes from east to west on thehorizontal plane a29, an altitude a22 of the Sun a01 gradually increasesto reach a zenith around noon and gradually decreases afterwards todisappear below the horizontal plane a29 in the evening. The Sun a01then rises in the east again after the Earth a02 revolves to an oppositeside. Around noon, an angle at which an altitude a22 of the Sun a01increases to the zenith based on a south point a25 while the Sun a01 ispassing a meridian a24 is referred to as a meridian altitude a23.

As illustrated in FIG. 3, sunlight a03 is incident, almost parallel, toany points of the Earth a02 because a distance between the Sun a01 andthe Earth a02 is far greater than a diameter of the Earth a02. Thesunlight a03 to be horizontally incident is observed at different anglesfrom each point of the Earth a02. Although an altitude a22 of the Suna01 to be observed in proximity to the equator a37 moves along a highpath passing adjacent to the zenith, an altitude a22 of the Sun a01 tobe observed decreases as a latitude a32 increases. Thus, the Sun a01observed in polar regions, for example, a North Pole a35 and a SouthPole a36, performs the diurnal motion along a low path passing adjacentto the horizon. As described in the foregoing, the meridian altitude a23varies depending on a latitude a32 of an observation point. Contrary toa case of the northern hemisphere, in a case of the southern hemisphere,a diurnal motion path a04 of the Sun a01 passes through the northern skyin lieu of the southern sky. In addition, when observing the meridianaltitude a23 based on the south point a25, a value of the meridianaltitude a23 exceeds 90° passing the zenith. Thus, in such a case, usingan altitude of lower culmination based on a north point a26 may bedesirable. Unless otherwise specified, example embodiments will bedescribed based on the northern hemisphere, and the solar tracker 1000may be identically applicable when a corresponding observed value isapplied to the case of the southern hemisphere.

The diurnal motion of the Sun a01 may vary depending on a latitude a32of an observation point, and a meridian altitude a23 may change based ona colatitude a33, which is a value obtained by subtracting a latitudea32 of an observation point from 90°. Here, a meridian altitude a23 ofthe Sun a01 to be observed from the Earth a02 may vary depending onwhere the Earth a02 is positioned in a revolution orbit in addition to alatitude a32 of an observation point. This is due to the Earth'srotation axis a34 being tilted at approximately 23.5° against arevolution axis. Although the tilted angle of the Earth's rotation axisa34 is invariant, a relative tilt direction with respect to the Sun a01varies depending on the position of the Earth a02 while the Earth a02revolves around the Sun a01 and thus, affects a meridian altitude a23 ofthe Sun a01 to be observed at an observation point of the Earth a02.

FIG. 4 illustrates a correlation between the relative tilt direction ofthe Earth's rotation axis a34 and a meridian altitude a23 in revolutionof the Earth a02. The correlation is illustrated in detail with anexample of a region in the northern hemisphere. In a region in thenorthern hemisphere, when a direction of the Earth's rotation axis a34is tilted for the northern hemisphere to face the Sun a01, the diurnalmotion path a04 of the Sun a01 rises and a meridian altitude a23increases and thus, a density of solar energy arriving per unit area ofthe horizontal plane a29 increases. Thus, a temperature of the region ismaintained to be high around the summer solstice a42 in which a meridianaltitude a23 becomes a maximum. In the region, such a season isclassified as summer. Conversely, on a cycle of revolution of the Eartha02, when the Earth's rotation axis a34 is tilted for the northernhemisphere to be less exposed to the Sun a01, a meridian altitude a23decreases. Thus, a temperature of the region is maintained low aroundthe winter solstice a44 in which a meridian altitude a23 becomes aminimum. In the region, such a season is classified as winter.

As illustrated in FIG. 4, the diurnal motion path a04 of the Sun a01changes based on a season. Each diurnal motion path a04 is generatedalong a circumference of a circular disk perpendicular to the Earth'srotation axis a34 on the celestial sphere a19, and circular disksincluding each diurnal motion path a04 are parallel to one another. Inthe spring equinox a41 or the autumn equinox a43, the diurnal motionpath a04 of the Sun a01 is generated along the equatorial plane a17 onthe celestial sphere a19. Here, the diurnal motion path a04 is preciselydivided, in half, into a path exposed above the horizontal plane a29 anda path remaining in an opposite side of the Earth a02. Thus, a period oftime during which the Sun a01 remains in the sky until the Sun a01disappears to the west after rising in the east is a half of the day. Inthe summer solstice a42, the path exposed above the horizontal plane a29in the circular disk perpendicular to the Earth's rotation axis a34 islonger, and a period of time during which the Sun a01 remains in the skyuntil the Sun a01 disappears to the northwest after rising in thenortheast is greater than or equal to 12 hours. In the winter solsticea44, the path exposed above the horizontal plane a29 in the circulardisk perpendicular to the Earth's rotation axis a34 is shorter, and aperiod of time during which the Sun a01 remains in the sky until the Suna01 disappears to the southwest after rising in the southeast is lessthan or equal to 12 hours. As a latitude a32 increases and, that is, acolatitudes a33 decreases, such a change in the diurnal motion path a04may be further discovered. For example, in an Arctic region of the NorthPole, where a colatitudes a33 is lower than the Earth's rotational axialtilt a05, a direction of the Earth's rotation axis a34 is nearlyperpendicular to the horizontal plane a29 and the diurnal motion patha04 of the Sun a01 is close to a circumferential motion moving along thehorizon. In the summer solstice a42, a situation in which a polar day ora white night during which the Sun a01 does not disappear from the skyand stays around the horizon all day may occur. In the winter solsticea44, a polar night that the night lasts all day while the Sun a01rotates below the ground may occur.

FIG. 5 illustrates a change in a meridian altitude a23 by an annualmotion of the Sun a01. Although the change is the same at anyobservation point on the Earth a02, the change occurs based on differentreference values based on a latitude a32 of an observation point. Ameridian altitude a23 increases starting from the spring equinox a41 andreaches a maximum in the summer solstice a42. Afterwards, the meridianaltitude a23 gradually decreases and returns to the same level as in thespring equinox a41 in the autumn equinox a43, and gradually decreasesagain to reach at a minimum in the winter solstice a44. Afterwards, themeridian altitude a23 increases again and recovers an original level inthe spring equinox a41. Although a reference value of the change in themeridian altitude a23 based on a solar term a40 varies depending on anobservation point, a cycle and a displacement of the change are thesame. That is, the cycle of the change in the meridian altitude a23 isapproximately 365 days during which the Earth a02 revolves around theSun a01. More accurately, the cycle is approximately 365.24219 daysbased on a solar time. In a case of the displacement of the change inthe meridian altitude a23, a maximum displacement occurring in thesummer solstice a42 and the winter solstice a44 may be equal to theEarth's rotational axial tilt a05. That is, when the Earth a02 makes onerevolution around the Sun a01 as one year progresses, the diurnal motionof the Sun a01 observed from the Earth a02 occurs approximately 365times, and a meridian altitude a23 of the Sun a01 observed from theEarth a02 gradually changes each day to pass through a maximum point anda minimum point depending on a solar term a40 and to return to anoriginal level of the meridian altitude a23, which forms one cycle of anannual motion. Here, a difference between the maximum point and theminimum point based on the reference value is approximately 23.5°, whichis the Earth's rotational axial tilt a05. The change in the meridianaltitude a23 of the Sun a01 at each observation point may be expressedas Equation 1.

Change in meridian altitude=reference value+change by annualmotion=90−latitude of observation point−change by annualmotion  [Equation 1]

For example, at an observation point located on the equator a36, ameridian altitude a23 changes, depending on a season, from a maximum113.5° to a minimum 66.5° based on 90° obtained by subtracting 0°, whichis a latitude a32 of the equator a36, from 90°. For another example, atan observation point located at the North Pole a35, a meridian altitudea23 changes from a maximum 23.5° to a minimum −23.5° based on 0°obtained by subtracting 90° , which is a latitude a32 of the North Polea35, from 90°. That is, a phenomenon called a polar night during whichthe Sun a01 is not observed may occur as the Sun a01 stays on thehorizon in spring and autumn and is positioned below the ground for sixmonths as winter progresses.

In an academic expression of a latitude a32 of an observation point,various expressions of the latitude a32 include a geodetic latitude, ageocentric latitude, and a geographic latitude. In Equation 1, an errormay not be significant despite use of the geodetic latitude expressed bysimplifying an ellipsoid of the Earth a02 to be a sphere. AlthoughEquation 1 uses a latitude a32 which is generally used in a geographicalcoordinate system, using a colatitude a33 in lieu of a latitude a32 maybe more desirable in a case of using a spherical coordinate system formathematics. In the case of using the spherical coordinate system formathematics, Equation 1 may be expressed as Equation 2.

Change in meridian altitude=colatitude of observation point+change byannual motion  [Equation 2]

The change occurring due to the annual motion of the Sun a01 inEquations 1 and 2 may be represented as a periodic function similar to atrigonometric function as illustrated in FIG. 5. A meridian altitude a23passes through a reference altitude corresponding to a colatitude a33 ofan observation point in the spring equinox a41 and monotonicallyincreases to have a maximum value in the summer solstice a42. A maximumdisplacement of the meridian altitude a23 is equal to the Earth'srotational axial tilt a05. Afterwards, the meridian altitude a23monotonically decreases, and returns to an original reference altitudeand is inflected in the autumn equinox a43 to have a minimum value inthe winter solstice a44. An angular displacement of the meridianaltitude a23 is also equal to the Earth's rotational axial tilt a05.Afterwards, the meridian altitude a23 increases again and returns to anoriginal altitude in the spring equinox a41. The annual motion of theSun a01 may be expressed as in Equation 3 through approximation based ona trigonometric function.

Change by annual motion=Earth's rotational axialtilt×sin(360°×(observation day−spring equinox day/365 days))  [Equation3]

The change in the meridian altitude a23 of the Sun a01 by the annualmotion based on the trigonometric function, which is finally obtained bysubstituting Equation 3 for Equation 2, may be expressed as in Equation4.

Change in meridian altitude=colatitude of observation point+Earth'srotational axial tilt×sin(360°×(observation day−spring equinox day/365days))  [Equation 4]

Equation 4 expresses a macroscopic change through approximation. Thus,to express a more precise change, various variables need to be includedtherein. For example, a difference in a revolution speed, or an orbitalspeed, between a perihelion and an aphelion which occurs because arevolution orbit of the Earth a02 is not a complete circle but anellipse may be considered. In consideration of an error of mechanicalcomponents included in a general type of the solar tracker 1000, factorsthat may have insignificant influence may be ignored from an engineeringperspective.

For describing a position of a celestial body including the Sun a01,using an equatorial coordinate system a10 based on a right ascension a11and a declination a12 may be more convenient than using a horizontalcoordinate system a20 based on an azimuth a21 and an altitude a22. Incomparison to the revolution orbit of the Earth a02, celestial bodiessuch as stars and galaxies astronomically observed may exist, ingeneral, hundreds of distance further than a distance between the Suna01 and the Earth a02. Thus, a general position of a celestial body isscarcely affected by the revolution of the Earth a02, and the positionof the celestial body may be expressed as a fixed point on the celestialsphere a19 using the equatorial coordinate system a10. The Sun a01 and aplanet in the solar system have a relatively shorter distance comparedto the revolution orbit of the Earth a02 and thus, a position of the Suna01 and the planet may change on the celestial sphere a19. Asillustrated in FIG. 6, the Sun a01 moves along the ecliptic a18 tiltedby the Earth's rotational axial tilt a05 from the equator plane a16 onthe celestial sphere a19, in accordance with the revolution of the Eartha02.

Brief descriptions of an apparatus and a device used in a field ofastronomy and space will be provided to assist the reader in gaining acomprehensive understanding of the solar tracker 100 described herein.Most astronomical devices used to observe stars, galaxies, nebulae, andthe like adopt the equatorial coordinate system a10 to continuouslytrack a celestial body and readily observe such a celestial body. Asillustrated in FIG. 6, in the equatorial coordinate system a10 which isa method of the celestial coordinate system, positions of celestialbodies fixed on the celestial sphere a19, which is an imaginary termindicating a huge sphere fixed in space and surrounding the Earth a02,are defined through spherical coordinates. The equatorial coordinatesystem a10 is a method of expressing a position of a celestial body onthe celestial sphere a19 based on a right ascension a11 measured in awest-east direction from a starting point, which is the springequinoctial point a45 at which the equatorial plane a17 meets theecliptic a18 on the celestial sphere a19, and based on a declination a12obtained by measuring an angle in a direction of the celestial axis a13extending the Earth's rotation axis a34 from the equatorial plane a17 ofthe celestial sphere a19 to the celestial sphere a19. As described inthe foregoing, in observing a celestial body such as galaxies andconstellations, an azimuth a21 and an altitude a22 may change dependingon an observation point when using the horizontal coordinate system a20.However, a right ascension a11 and a declination a12 may be expressed asa fixed value irrespective of an observation point when using theequatorial coordinate system a10. Thus, a celestial body map arrangedbased on a right ascension a11 and a declination a12 is widely used inthe field of astronomy, and an observer may more readily find a targetcelestial body within a view of a telescope by installing anastronomical telescope in an equatorial mount and adjusting a rightascension a11 and a declination a12.

The Earth a02 rotates one time each day on the celestial sphere a19fixed in space. To eyes of an observer in the Earth a02, constellationson the celestial sphere a19 appear to gradually rotate from east to westbased on a time. Such a rotation is referred to as a diurnal motion of acelestial body. A speed of the rotation corresponds to a rotation speedof the Earth a02, and the diurnal motion is performed at an angularvelocity of approximately 15° per hour. Thus, although an observer findsone constellation in the wide night sky, the constellation appears togradually flow to the west. Such a phenomenon may be more readilyobserved when magnifying a narrow area through an astronomicaltelescope. Although an observer secures a target celestial body to beobserved within a view of the observer, the secured target celestialbody may immediately disappear from the view when the observer fails tomove a direction of the telescope from east to west. In a case of ageneral type telescope adjusting an azimuth a21 and an altitude a22,simultaneously adjusting two rotation shafts is required to track acelestial body performing a diurnal motion. In a case of a telescopeusing an equatorial mount, an observer may conveniently observe acelestial body for a long period of time while offsetting a diurnalmotion of the celestial body as illustrated in FIG. 6 by graduallyturning a rotation shaft for a right ascension a11 while fixing arotation shaft for a declination a12.

When observing the Sun a01, dissimilar to other celestial bodies, aposition of the Sun a01 gradually changes on the celestial sphere a19,the Sun a01 gradually moves along the ecliptic a18 and makes onerevolution along the celestial sphere a19 each year. A speed of therevolution of the Sun a01 around the celestial sphere a19 is merely lessthan or equal to approximately 1° per day and thus, may be ignored whenobserving the Sun a01 for a short period of time. That is, whenobserving the Sun a01, the Sun a01 may be observed by ignoring a changein a declination a12 and fixing the rotation shaft for a declinationa12, and gradually turning only the rotation shaft for a right ascensiona11. However, when observing the Sun a01 for a long period of time,errors may be accumulated as days pass and thus, handling such an issueis necessary. Thus, offsetting the diurnal motion by turning therotation shaft for a right ascension a11 and simultaneously offsettingthe annual motion by turning the rotation shaft for a declination a12 isrequired without ignoring a change in the declination a12 of the Suna01. The change in the declination a12 of the Sun a01 by the annualmotion occurs while the Sun a01 travels along the ecliptic a18 titled onthe celestial sphere a19. Such a change corresponds to the change in themeridian altitude a23 represented in Equation 3.

The solar tracker 1000 according to example embodiments of the presentinvention will be described in detail with reference to FIG. 1. Thesolar tracker 1000 is specially designed to daily track a change in aright ascension a11 of the Sun a01 occurring due to a diurnal motion,and also automatically correct a change in a declination a12 of the Suna01 occurring due to an annual motion, in order to solve an error of thedeclination a12 accumulated for a long period of time. Based on acorrelation between the right ascension a11 and the declination a12 ofthe Sun a01 traveling along the ecliptic a18 on the celestial spherea19, the solar tracker 1000 includes a declination actuation mechanism400 that may allow a right ascension rotation shaft 100 and adeclination rotation shaft 300 to be in a mechanically dependantrelationship to track the diurnal motion of the Sun a01 by rotating theright ascension rotation shaft 100 through a right ascension rotationactuator 200 and to automatically compensate for the change in thedeclination a12 of the Sun a01 by transferring a portion of rotationalpower of the right ascension rotation actuator 200 to the declinationrotation shaft 300.

The solar tracker 1000 includes the right ascension rotation shaft 100,the right ascension rotation actuator 200, the declination rotationshaft 300, and the declination actuation mechanism 400. Hereinafter,these components will be described in detail, and an applicable methodusing additional components to improve convenience of exampleembodiments of the present invention will also be described in detail.

FIG. 1 illustrates an example of the solar tracker 1000 according to anembodiment of the present invention. Main components to be connectedfrom the ground up to a solar light collector 600 are described asfollows. A support 510 is fixed to the ground and a pillar 520 isconnected thereto, and at an end thereof a right ascension rotationsupport 530 is installed at a suitably tilted angle. The right ascensionrotation shaft 100 is installed in the right ascension rotation support530, and a declination rotation support 540 is connected thereto forunrestricted rotation. The declination rotation support 540 and a lightcollector holder 550 are installed to enable the unrestricted rotationthrough the declination rotation shaft 300, and the light collector 600is attached to the light collector holder 550. The right ascensionrotation actuator 200 is provided to actuate the right ascensionrotation shaft 100, and the declination actuation mechanism 400 isprovided to transfer a portion of driving power of the right ascensionrotation actuator 200 to the declination rotation shaft 300.

The example illustrated in FIG. 1 is mechanically equivalent to2-degrees of freedom (DOF) series-type two-bar linkage, which isillustrated in (b) of FIG. 8. That is, the support 510, the pillar 520,and the right ascension rotation support 530 are formed to be a baselink L0 as a single rigid body connected to the ground, and thedeclination rotation support 540 is formed to be a first link L1 and thelight collector holder 550 functions as a second link L2. The rightascension rotation shaft 100 and the declination rotation shaft 300operate as a first joint J1 connecting the base link L0 to the firstlink L1 and as a second joint J2 connecting the first link L1 to thesecond link L2, respectively. As described in the foregoing, amechanical form of the solar tracker 1000 adopts a 2-DOF mechanism, andin actuality, is defined as a 1-DOF mechanism because the first joint J1and the second joint J2 operate dependently on each other and makedependent movements. Hereinafter, a method of installing and connectingcomponents included in the links L0, L1, and L2, and the joints J1 andJ2 will be described first, and a method of dependently actuating theright ascension rotation shaft 100 and the declination rotation shaft300 corresponding to the joint J1 and the joint J2 will be described indetail.

According to example embodiments, a frame 500 is formed to allow theright ascension rotation shaft 100 to be installed in parallel with theEarth's rotation axis a34, and allow the declination rotation shaft 300to be installed perpendicularly to the right ascension rotation shaft100. Thus, the frame 500 is formed to robustly support the two rotationshafts so that the two rotation shafts smoothly move in predetermineddirections. The frame 500 includes the support 510, the pillar 512, theright ascension rotation support 530, the declination rotation support540, and the light collector holder 550. The support 510 and the pillar520 include an adjuster configured to adjust an azimuth a21 and analtitude a22 to install the right ascension rotation shaft 100 to beparallel with the Earth's rotation axis a34. An example of using onepillar 520 will be described with reference to (a) of FIG. 7. Aftersolidifying the ground and installing the support 510 on which screwholes are processed and fixing the support 510 to the ground, the pillar520 is set up on the support 510 fixed to the ground. Here, bolts arefastened along the screw holes on a side face of the support 510 tochange an azimuth a21 for the pillar 520 to face north and to readilyadjust the right ascension rotation shaft 100 to be parallel with theEarth's rotation axis a34.

The right ascension rotation support 530 is installed on the pillar 520and the right ascension rotation shaft 100 is fixed. Here, an adjusterconfigured to adjust an altitude a22 of the right ascension rotationshaft 100 is provided based on a latitude a32 of an installationlocation. As illustrated in FIG. 7, rotation is enabled when the pillar520 is connected to the right ascension rotation support 530, and screwholes are processed on a flange to fix the right ascension rotationsupport 513 to the pillar 520 with the right ascension rotation support530 suitably tilted based on the latitude a32 of the installationlocation. Thus, as illustrated in FIG. 6, a direction of the Earth'srotation axis a34 and a direction of the right ascension rotation shaft100 are formed to be parallel with each other based on the latitude a34of the installation location by adjusting a rotation direction of thepillar 520 fixed to the support 510 and a tilt of the right ascensionrotation support 530.

As illustrated in (b) of FIG. 7, the frame 500 is formed using twopillars 520, for example, a pillar 520 a and a pillar 520 b. The twopillars 520 a and 520 b are set up on the support 510, and both ends ofthe right ascension rotation shaft 100 are connected to the two pillars520 a and 520 b. To adjust an azimuth a21 of the right ascensionrotation shaft 100, the two pillars 520 a and 520 b are adjusted toaccurately face a south-north direction while the pillar 520 a or thepillar 520 b moves to an east-west direction. To adjust an altitude a22of the right ascension rotation shaft 100, a height of the pillar 520 aor the pillar 520 b is adjusted to suitably change an angle formedbetween the right ascension rotation shaft 100 and the ground. In a caseof the northern hemisphere, a height of the pillar 520 b in the north isinstalled to be higher than a height of the pillar 520 a in the southbased on a latitude a32. Conversely, in a case of the southernhemisphere, the height of the pillar 520 b in the north is fixed to belower than the height of the pillar 520 a in the south. Here, the rightascension rotation shaft 100 may be bent while changing the height ofthe pillar 520 a or the pillar 520 b. In such a case, a deformation bythe bending may be resolved by forming the pillars to be rotatable in adirection towards which the right ascension rotation shaft 100 isdeflected at both ends thereof.

Examples of the support 510 and the pillar 520 are provided herein, andvariously modified examples that may adjust an azimuth a21 and analtitude a22 of the right ascension rotation shaft 100 may beapplicable.

According to an embodiment, the right ascension rotation shaft 100 isinstalled in parallel with the Earth's rotation axis a34, and isconfigured to offset a diurnal motion of the Sun a01 occurring due torotation of the Earth a02 and to track a position of the Sun a01 thatrises in the east and sets in the west every day while rotating in anopposite direction to a direction of the rotation of the Earth a02 at anangular velocity corresponding to the rotation of the Earth a02. Inaddition, the declination rotation shaft 300 is installedperpendicularly to the right ascension rotation shaft 100 and positionedin parallel with the equatorial plane a17 of the celestial sphere a19,and is configured to offset an annual motion of the Sun a01 occurringdue to revolution of the Earth a02 and to compensate for a change in ameridian altitude a23 of the Sun a01 that occurs depending on a solarterm a40 as illustrated in FIG. 4 while in turn rotating upwards anddownwards at the Earth's rotational axial tilt a05 based on a cycle ofapproximately 365 days.

As illustrated in FIG. 8, the right ascension rotation shaft 100 isinstalled at an end of the right ascension rotation support 530 fixed tothe ground through the support 510 and the pillar 520, and thedeclination rotation support 540 is connected for unrestricted rotation.The declination rotation shaft 300 is installed in the declinationrotation support 540 to be perpendicular to the right ascension rotationshaft 100, and the declination rotation support 540 is connected to thelight collector holder 550 through the declination rotation shaft 300.When the declination rotation support 540 rotates along the declinationrotation shaft 300, only an angle of a declination a12 may changewithout a change in an angle of a right ascension a11 to which theinstalled light collector 600 faces. In addition, when the rightascension rotation shaft 100 is installed in parallel with the Earth'srotation axis a34, only the angle of the right ascension a11 may changeindependently and the angle of the declination a12 may not changealthough the declination rotation support 540 rotates along the rightascension rotation shaft 100 and the attached light collector holder 550and the installed light collector 600 rotate accordingly. Thus,coordinates of the right ascension a11 and the declination a12 on thecelestial sphere a19 to which the attached light collector 600 faces maybe independently adjusted and, further, unrestrictedly adjusted to alldirections of the celestial sphere a19 by installing the right ascensionrotation shaft 100 to correspond to the Earth's rotation axis a34 basedon a location at which the solar tracker 1000 is installed and byadjusting each of the right ascension rotation shaft 100 and thedeclination rotation shaft 300 which are perpendicularly installed withrespect to each other. FIG. 6 also illustrates an example of a case inwhich the right ascension rotation shaft 100 is installed in parallelwith the Earth's rotation axis a34, and an operation principle oftracking a position fixed to the celestial sphere a19 for a long periodof time while rotating in an opposite direction to a rotation directionof the Earth a02.

According to an embodiment, a balance weight 560 is configured to allowa load to be transferred to the right ascension rotation shaft 100 orthe declination rotation shaft 300 to be balanced and thus, run thesolar tracker 1000 using equal rotational power at any angle. Althoughthe balance weight 560 may not be an integral component to implementfunctions of the present invention, the balance weight 560 may be usefulto improve efficiency of the solar tracker 1000.

A load to be applied to the right ascension rotation shaft 100 and thedeclination rotation shaft 200 may vary depending on forms and weightsof the declination rotation support 540, the light collector holder 550,the solar light collector 600, and various attached components. When theweights of such components are not suitably distributed from a center ofeach rotation shaft, driving power required due to a change in an angleof a rotation shaft may change. Thus, a considerable amount of drivingpower may be required for movement in an opposite direction despite aneasy rotation to one direction and accordingly, efficiency of anactuator used may decrease.

Thus, the weights need to be suitably distributed along each rotationshaft to be well-balanced without being inclined to one side so that arotation shaft may smoothly operate using an equal torque at any angles.In general, a weight of the solar light collector 600 accounts for alarge portion of a total weight of the solar tracker 1000 and thus,structural balance may not be readily achieved. As illustrated in FIG.9, a counter balancing weight which counterbalances a weight of anobject having a great mass is installed in an opposite side to achieve abalance and allows each rotation shaft to smoothly rotate in eachrotation shaft direction. A right ascension balance weight 561 having asuitable weight is attached to suitably distribute weights in both sidesfrom a center of the right ascension rotation shaft 100, and adeclination balance weight 562 having a suitable weight is attached tosuitably distribute weights in both sides from a center of thedeclination rotation shaft 300 as necessary. When a whole mechanism iswell-balanced from a center of rotation of each rotation shaft, equaltorque may be applied to rotation at any angles and thus, each rotationshaft may smoothly rotate using a lower amount of power.

To implement the solar tracker 1000, a method of constructing a 2-DOFmechanism using the right ascension rotation shaft 100 and thedeclination rotation shaft 300 is described above. Hereinafter, a methodof operating an entire mechanism with 1-DOF through a dependentrelationship between two rotation shafts will be described in detail.

According to an embodiment, the right ascension rotation actuator 200 isconfigured to provide rotational power to the right ascension rotationshaft 100 so that the right ascension rotation shaft 100 may track adiurnal motion of the Sun a01 traveling from east to west every day onthe celestial sphere a19 while traveling at an angular velocity of 15°per hour corresponding to a rotation velocity of the Earth a02.

The right ascension rotation actuator 200 will be described in detailwith reference to an example illustrated in FIG. 10. The right ascensionrotation actuator 200 includes an actuator 210 and a right ascensionreducer 220. The actuator 210 of a rotating type is installed in thedeclination rotation support 450. The right ascension reducer 220includes a right ascension direct connection reducer 221 directlyconnected to the actuator 210, and a right ascension worm gear 222 and aright ascension worm wheel 223. Rotational power generated from theactuator 210 is amplified through the right ascension direct connectionreducer 221 to operate the right ascension worm gear 222. The rightascension worm gear 222 is interlocked with the right ascension wormwheel 223 fixed to the right ascension rotation support 530 to operatethe declination rotation support 540 and thus, the right ascensionreducer 220 rotates along the right ascension rotation shaft 100. Asillustrated in FIG. 10, the actuator 210 is fixed to the declinationrotation support 540 to readily implement the declination actuationmechanism 400 to be described hereinafter and thus, the actuator 210rotates along with the declination rotation support 540. As necessary,the actuator 210 and the right ascension worm gear 222 are installed inthe right ascension rotation support 530 and the right ascension wormwheel 223 is fixed to the declination rotation support 540 to design theactuator 210 not to move.

The right ascension rotation actuator 200 allows the right ascensionrotation shaft 100 to rotate from east to west every day. A velocity ofsuch a rotation needs to correspond to a rotation velocity of the Eartha02, for example, one round per day which is an angular velocity ofapproximately 15° per hour, and to output a torque to generate asufficient acceleration force for rapid operation. Various rotatingtypes of actuators 210 may be used as the actuator 210, and a linearactuator 210 may be used as the actuator 210 in combination with asuitable converter such as a crank-slider. In a case of using a generalelectric motor, using the right ascension reducer 220 may be suitablebecause the electric motor has a fast rotation speed and a small torque.Here, an integral-type reducer directly connected to the electric motormay be adopted and additional reduction may be externally applied asnecessary. In a case of a high reduction gear ratio, using a planetarygear and a harmonic drive may be used. Also, a spur gear may be combinedto form an input shaft and an output shaft to be parallel with eachother, and alternatively a bevel gear or a worm gear may be used to formthe input shaft and the output shaft not to be parallel with each other.In such an alternative case, a power transfer path may be diversifiedand thus, a more unconstrained designing method may be applied. Gears invarious sizes may be combined, and a timing belt or a cable may be usedto reduce an error that may be caused by a backlash. In addition tovarious methods described in the foregoing, variously modified forms ofreducers which are used in industrial sites may be used for the rightascension reducer 220. Alternatively, in a case of a sufficient torqueof the actuator 210 used, the right ascension reducer 220 may be removedand the actuator 210 may be directly connected to the right ascensionrotation shaft 100.

The declination actuation mechanism 400 is configured to allow the rightascension rotation shaft 100 and the declination rotation shaft 300 tohave a mechanically dependent relationship based on a correlationbetween a diurnal motion and an annual motion of the Sun a01, and allowthe declination rotation shaft 300 to reciprocatingly rotate upwards anddownwards to compensate for the annual motion of the Sun a01 inconjunction with the right ascension rotation shaft 100 rotating totrack the diurnal motion of the Sun a01.

The right ascension rotation shaft 100 moves along the diurnal motion ofthe Sun a01 from east to west every day, by the right ascension rotationactuator 200. Meanwhile, a portion of driving power of the rightascension rotation actuator 200 is transferred to the declinationrotation shaft 300 through the declination actuation mechanism 400.Thus, the declination rotation shaft 300 moves dependently on the rightascension rotation shaft 100. Here, the declination actuation mechanism400 is configured to allow the declination rotation shaft 300 to movesimilarly to the description provided with reference to Equation 4 whilethe right ascension rotation shaft 100 tracks the diurnal motionapproximately 365 times.

As illustrated in FIG. 11, the declination actuation mechanism 400includes a declination reducer 410 which has, as an input, one point ina path through which power is transferred from the right ascensionrotation actuator 200 to the right ascension rotation shaft 100, and areciprocating rotation conversion mechanism 420 which transfers arotational motion of an output shaft of the declination reducer 410 andconverts the rotational motion to a reciprocating rotational motion ofthe declination rotation shaft 300. In FIG. 11, driving power isextracted from one point in the right ascension reducer 220. In detail,rotational power of the right ascension worm gear 222 is transferred tothe declination reducer 410.

In determining a reduction gear ratio of the declination reducer 410,the reciprocating rotation conversion mechanism 420 may be readilydesigned by allowing the output shaft of the declination reducer 410 torotate one revolution with respect to an amount of rotation generatedwhile the right ascension rotation shaft 100 tracks the diurnal motionof the Sun a01 approximately 365 times. As illustrated in FIG. 11, afour-bar linkage is formed by determining the reduction gear ratio atwhich the output shaft of the declination reducer 410 makes one rotationfor approximately 365 days, fixing a crank 421 to the output shaft ofthe declination reducer 410, fixing a rocker 422 rotating upwards anddownwards along the annual motion of the Sun a01 to the declinationrotation shaft 300, and including therein a connecting rod 423connecting one end of the crank 421 to one end of the rocker 422. InFIG. 11, a pin joint is provided on a side face of the light collectorholder 550 for the light collector holder 550 to function as the rocker422.

An operation principle of the reciprocating rotation conversionmechanism 420 formed as the four-bar linkage is as follows. Therotational motion of the crank 421 is converted to the reciprocating upand down rotational motion of the rocker 422 through the connecting rod423. When the crank 421 makes one rotation through the declinationreducer 410 while the right ascension rotation shaft 100 tracks thediurnal motion approximately 365 times, the rocker 422 in turn rotatesupwards and downwards on a cycle of approximately 365 days.

FIG. 12 illustrates an example of a change in an angle of the lightcollector holder 550 attached to the declination rotation shaft 300based on a solar term a40. The crank 421 rotates approximately ¼ everythree months and rotates approximately 90° each solar term a40. Thecrank 421 adjusts the light collector holder 550 to be positioned at atop dead center and a bottom dead center in the summer solstice a42 andthe winter solstice a44, respectively. Thus, the light collector holder550 is positioned at a neutral point in the spring equinox a41. Afterthe spring equinox a41, the crank 421 pulls the connecting rod 423, andan angle of the light collector holder 550 gradually increases andreaches a maximum angle in the summer solstice a42. When the crank 421pushes the connecting rod 423 upwards while passing the top dead centerin the summer solstice a42, an angle of the light collector holder 550gradually decreases and returns to the neutral point in the autumnequinox a43. After approximately nine months, the crank 421 reaches thebottom dead center in the winter solstice a44 and the angle becomes aminimum angle and afterwards, the crank 421 pulls the connecting rod 423downwards and the angle of the light collector holder 550 increases.After approximately one year, the crank 421 makes one complete rotationand the light collector holder 550 returns to the neutral point when thespring equinox a41 arrives again.

Here, a relative length of the crank 421, the connecting rod 423, andthe rocker 422, and a position of each connection joint need to besuitably determined to allow a maximum angle at which the declinationrotation shaft 300 reciprocatingly rotates to be an angle in an upperand lower sides corresponding to the Earth's rotational axial tilt a05.An adjuster 424 that adjusts a position of a joint and a link length maybe provided to the crank 421, the rocker 422, or the connecting rod 423to finely adjust a motional displacement and a sectional speed of thereciprocating up and down rotational motion of the rocker 422. Thus, thedeclination rotation shaft 300 may operate similarly to the change inthe meridian altitude a23 of the Sun a01 described with reference toEquation 4.

In actual operation of the solar tracker 1000, an amount of rotation ofthe right ascension rotation shaft 100 varies depending on a season andaccordingly, an angle accumulated in the declination rotation shaft 300varies. For example, in the summer, an amount of rotation of the rightascension rotation shaft 100 increases and a change of the declinationrotation shaft 300 is accelerated. Conversely, in the winter, anaccumulated angle to be transferred to the declination rotation shaft300 is reduced. In addition, a difference in a revolution speed of theEarth a02 between an aphelion and a perihelion occurs and thus, an errorfor a short period of time may become greater. To consider such achange, the adjuster 424 adjusting a position of a joint and a linklength is used to finely adjust the motion of the rocker 422. In anexample of a change in a rotation angle of the crank 421 and areciprocating rotation angle of the light collector holder 550 asillustrated in FIG. 12, a section from the spring equinox a41 to theautumn equinox a43 through the summer solstice a42 is longer than asection from the autumn equinox a43 to the spring equinox a41 throughthe winter solstice a44. In the example of FIG. 12, the crank 421 is notsimply designed to rotate ¼ rounds at each solar term a40, but speciallydesigned to vary a sectional speed based on a change in the revolutionspeed at the aphelion and the perihelion and the equation of time.

Although the four-bar linkage is provided as an example of thereciprocating rotation conversion mechanism 420, various mechanismmodifications, for example, a crank-slider type, a cam follower type,and a five-bar linkage, may be applied to achieve functions of thereciprocating rotation conversion mechanism 420 to simulate thecorrelation between the diurnal motion and the annual motion. Inaddition, in various methods of applying modified examples of thereciprocating rotation conversion mechanism 420, although a dependentrelationship between the rotational motion of the right ascensionrotation shaft 100 and the reciprocating up and down rotational motionof the declination rotation shaft 300 differs from the descriptionprovided with reference to Equation 4, the difference may not restrictan operation of the solar tracker 1000 unless a range of the differenceis large.

A coupling 430 is provided to remove the dependent relationship betweenthe right ascension rotation shaft 100 and the declination rotationshaft 300 as necessary. In an initial installation of the solar tracker1000, adjusting an angle of the declination rotation shaft 300 to besuitable for a corresponding solar term a40 based on an installationtime is necessary. In a long-term operation of the solar tracker 1000,an error may occur between an angle of the declination rotation shaft300 and an actual declination a12 of the Sun a01 and thus, an angle ofthe declination rotation shaft 300 may be reset to eliminate such anerror. The right ascension rotation shaft 100 and the declinationrotation shaft 300 of the solar tracker 1000 have a correlation by beingdependent on each other through the declination actuation mechanism 400,and such a correlation may be an inconvenience in resetting an angle ofthe declination rotation shaft 300. To solve such an inconvenience, ameans may be provided to remove such a dependent relationship betweenthe right ascension rotation shaft 100 and the declination rotationshaft 300 as necessary and independently adjust the declination rotationshaft 300. Driving power used to actuate the declination rotation shaft300 is supplied from the right ascension rotation actuator 200 andtransferred through a reducer or a linkage. Thus, the coupling 430 isinstalled at one point in a path through which power is transferred fromthe right ascension rotation actuator 200 to the declination rotationshaft 300, and is configured to selectively connect or block rotationalpower to be transferred and apply or remove the dependent relationshipbetween the right ascension rotation shaft 100 and the declinationrotation shaft 300.

Referring to FIG. 13, the coupling 430 is installed in a portionconnecting a final output shaft of the declination reducer 410 to thecrank 421 of the reciprocating rotation conversion mechanism 420. Whenreleasing the coupling 430, an angle of the light collector holder 550may be unrestrictedly changed by adjusting a rotation angle of the crank421 without affecting the right ascension rotation shaft 100.

According to an embodiment, a one-way clutch 450 is provided to allowonly one-way rotational motion of the right ascension rotation shaft 100to interwork with the declination rotation shaft 300. In general, due toa large volume of the light collector 600 attached to the solar tracker1000, an interference may occur in a surrounding environment. Thus, theright ascension rotation shaft 100 may perform a two-way reciprocatingrotation without continuous rotations while avoiding such aninterference. As illustrated in FIG. 14, in the daytime, the rightascension rotation shaft 100 makes a half rotation until the Sun a01sets in the west after the Sun a01 rises in the east. Conversely, in thenighttime, the right ascension rotation shaft 100 returns to the eastafter reversely rotating in an opposite direction and tracing up a paththrough which the right ascension rotation shaft 100 passes in thedaytime, and waits for the next morning to track the Sun a01 again. Inthe interworking between the declination rotation shaft 300 and theright ascension rotation shaft 100, the reverse rotational motion of theright ascension rotation shaft 100 in the nighttime needs to be ignored,and an amount of the normal rotation used to track the Sun a01 from eastto west in the daytime needs to be selectively extracted and transferredto the declination rotation shaft 300 through the declination actuationmechanism 400.

Using the one-way clutch 450, such a one-way rotational power may beselectively extracted from the two-way reciprocating rotational motion.Thus, only a rotation component that tracks the diurnal motion of theSun a01 from east to west in the daytime may be extracted, and thereverse rotational motion of the right ascension rotation shaft 100 inthe nighttime may not be transferred to the declination rotation shaft300. FIG. 13 illustrates an example of the declination actuationmechanism 400 including the one-way clutch 450. In the example of FIG.13, the one-way clutch 450 is installed at a front end of the inputshaft of the declination reducer 410 to allow only one-way rectifiedrotation component to be input to the declination reducer 410. Inprinciple, the one-way clutch 450 may be installed at any point at whichthe driving power is transferred from the right ascension rotationactuator 200 to the declination rotation shaft 300 to achieve the samefunctions as described in the foregoing. In a case of the lightcollector 600 of a small volume and absence of the interference to thesurrounding environment, using the one-way clutch 450 may be unnecessarybecause the right ascension rotation shaft 100 may track the Sun a01while continuously rotating.

As illustrated in FIG. 14, in the solar tracker 1000 using the one-wayclutch 450, an amount of diurnal rotation occurring while the rightascension rotation shaft 100 normally tracks the diurnal motion of theSun a01, exclusive of the reverse rotation to return to the east in thenighttime, is approximately a half rotation per day. Here, a reductiongreat ratio at which the crank 421 of the declination actuationmechanism 400 rotates approximately 1/365 times needs to be set withrespect to the half rotation per day. Since the half rotation variesdepending on a surrounding topography, a season, a mechanical motionrange of the right ascension rotation shaft 100, and the like, thedeclination reducer 410 or a reduction ratio adjuster 440 needs to besuitably adjusted based on an installation environment.

The reduction ratio adjuster 440 is provided to adjust a ratio of anamount of rotation of the declination rotation shaft 300 to therotational motion of the right ascension rotation shaft 100. In thesolar tracker 1000, the declination rotation shaft 300 graduallyoperates each day in conjunction with an amount of rotation of the rightascension rotation shaft 100 used to track the diurnal motion of the Suna01 each day. An amount of rotation of the declination rotation shaft300 which is gradually accumulated each day may be merely 23.5° perthree months. However, when the reduction gear ratio of the declinationreducer 410 is not accurately set, an error may be accumulated duringthe long-term use and thus, accuracy may decrease. When the rightascension rotation shaft 100 operates to perform the reciprocatingrotation in opposite directions in the daytime and in the nighttime, amotional range of the right ascension rotation shaft 100 may changedepending on a surrounding environment and an installation condition andalso, an additional error may occur when operating the one-way clutch450. For example, in a mountainous region dissimilar to a beach aroundwhich no obstacles are present, a period of time used to track the Suna01 in the daytime may be considerably decrease and thus, reducing amotional range of the right ascension rotation shaft 100 may benecessary. In a case of installing multiple solar trackers 1000, anamount of rotation of the right ascension rotation shaft 100 may berestricted to dispose the multiple solar trackers 1000 not to coversunlight to one another. Since an error may be accumulated due to thelong-term operation, the reduction ratio adjuster 440 is provided toreadily adjust the reduction gear ratio of the declination reducer 410.

In the example of the reduction ratio adjuster 440 illustrated in FIG.13, rotational power is extracted from the right ascension worm gear 222of the right ascension rotation actuator 200 and the extracted power isinput to the reduction ratio adjuster 440. A pulley-belt transfer deviceused mainly for a continuously variable transmission and changing arotation radius may be used as an example of the reduction ratioadjuster 440. Here, two rotation wheels having respective inclinedplanes are installed to face to each other to form a V-groove pulley,and a distance between the two rotation wheels is adjustable. When thedistance of the V-groove pulley increases, a valid rotation radius inwhich a belt operates decreases. Conversely, when the distance of theV-groove pulley decreases, the valid rotation radius increases. Thus,the reduction gear ratio may be adjusted to increase and decrease.Alternatively, the reduction gear ratio may be adjusted by installing amulti-stepped pulley having different radii at both shafts and hanging abelt on a suitable position. Alternatively, various devices may beprovided to adjust a radius of a pulley, and other mechanisms inaddition to the pulley may be provided to adjust the reduction gearratio.

In adjusting the reduction gear ratio, matching a one year cycle of thereciprocating up and down rotational motion may be more necessary ratherthan considering a short-term error of the declination rotation shaft300. In general, an amount of rotation of the right ascension rotationshaft 100 varies depending on a season and an angle to be accumulated inthe declination rotation shaft 300 may vary accordingly. For example, inthe summer when an amount of rotation of the right ascension rotationshaft 100 increases, a change in the declination rotation shaft 300 maybe further accelerated. Conversely, in the winter, an accumulated angleto be transferred to the declination rotation shaft 300 may decrease.Thus, although an error occurs when a short-term change in thedeclination rotation shaft 300 deviates from a curve provided inEquation 4, an error accumulated in the summer and the winter may beoffset and the error may be autonomously removed after the one yearcycle elapses.

A declination display device 460 is provided to display, as an angle, adeclination a12 in a direction to which the light collector 600 attachedto the solar tracker 1000 faces the celestial sphere a19. A solar termdisplay device 470 is provided to convert, to a solar term a40, adeclination a12 in the direction to which the light collector 600attached to the solar tracker 1000 faces the celestial sphere a19, anddisplay the solar term a40. At an initial installation of the solartracker 1000, a direction of the light collector holder 550 and thelight collector 600 attached thereto needs to match to a declination a12of the Sun a01 by suitably adjusting an angle of the declinationrotation shaft 300 based on an installation time. A difference betweenan angle of the declination rotation shaft 300 and an actual declinationa12 of the Sun a01 currently staying in the sky may occur due to thelong-term operation of the solar tracker 1000, and correcting such adifference may be necessary. FIG. 15 illustrates an example of thedeclination display device 460 configured to display an angle of thedeclination rotation shaft 300. The light collector holder 550 is in aneutral state in which the light collector holder 550 is parallel withthe right ascension rotation shaft 100 in the spring equinox a41 and theautumn equinox a43 in which a declination a12 of the Sun a01 becomes 0°.In the example of the declination display device 460, a declinationmeasuring pointer 461 is fixed to the light collector holder 550rotating along with the light collector 600, and a declination marking462 is attached to the declination rotation support 540 to measure anangle formed between the light collector holder 550 and the rightascension rotation shaft 100. Thus, a declination a12 on the celestialsphere a19 to which the solar tracker 1000 actually faces may be readilyread through the declination display device 460.

In the long-term operation of the solar tracker 1000, verifying accurateoperation of the solar tracker 1000 may be important. However,performing a comparison of an actual direction of the solar tracker 1000measured through the declination display device 460 and a declinationa12 of the Sun a01 based on a measurement time may be inconvenient. Asdescribed with reference to Equation 4, since a declination a12 of theSun a01 and a solar term a40 have a correlation and most countries inthe world use a solar calendar based on a declination a12 of the Sun a01as a method of counting dates, a declination a12 of the Sun a01 may bereadily converted to dates on the calendar. Thus, an error may be moreintuitively verified by, rather than displaying an actual direction ofthe solar tracker 1000 as an angle through the declination displaydevice 460, converting the angle to a solar term a40 in which the solartracker 1000 tracks and displaying the solar term a40. FIG. 15 alsoillustrates an example of the solar term display device 470 configuredto convert an angle of the declination rotation shaft 300 to a solarterm a40 and display the solar term a40. In the example, a solar termmeasuring pointer 471 is installed in the crank 421 connected to theoutput shaft of the declination reducer 410 to rotate together, and asolar term marking 472 is provided in the declination rotation support540 to convert an amount of rotation of the crank 421 to a correspondingsolar term a40 and read the solar term a40. For example, when the crank421 is designed to make one rotation per year, a correlation between anamount of rotation of the crank 421 and a solar term a40 is illustratedas in FIG. 15. The solar term marking 472 is broadly divided into foursolar terms, for example, the spring equinox a41, the summer solsticea42, the autumn equinox a43, and the winter solstice a44, and displaysthe solar terms and rotates along with the crank 421. Thus, a solar terma41 corresponding to a current rotation angle of the crank 421 may beread through the solar term measuring pointer 471. More precisemeasurement may be enabled using more detailed markings of the solarterm marking 472 by dividing the solar term marking 472 into, forexample, 12 solar terms, each month, and each day, in addition to theillustrated four solar terms. In addition, intervals between themarkings may be modified based on a case that an amount of rotationaccumulated in the summer differs from an amount of rotation accumulatedin the winter. Based on a change in an angle of the crank 421illustrated in FIG. 12, a summer section is designed to be longer than awinter section and thus, intervals between the markings in the summerare designed to be longer than intervals in the markings in the winter.

When the solar tracker 1000 is appropriately installed and an error issuitably corrected, the right ascension rotation shaft 100 graduallymoves along the diurnal motion of the Sun a01, and the solar termmarking 472 through which the solar term measuring pointer 471 passesincreases each day. After one year passes over the four solar terms, thesolar term marking 472 makes one complete rotation and returns to anoriginal date. Through the solar term display device 470, an angle ofthe declination rotation shaft 300 may be periodically converted to atemporal solar term a40, and a tracking error of the declinationrotation shaft 300 may be intuitively verified based on a comparison ofthe solar term a40 and a current date on the calendar. In addition, anaccurate tracking may be enabled by applying, to the reduction ratioadjuster 440, a trend of the tracking error which is gradually putforward or backward.

The declination display device 460 and the solar term display device 470are identical in principle without a difference in a unit of markings.When the markings of the declination display device 460 are displayed asa solar term a40, the declination display device 460 may be used as thesolar term display device 470. Alternatively, the declination displaydevice 460 and the solar term display device 470 may be integrated intoone display device by indicating both the angle and the solar term a40.In addition, since all driving shafts in a power transfer path throughwhich driving power generated from the right ascension rotation actuator200 is transferred to the declination rotation shaft 300 through thedeclination actuation mechanism 400 include information on a declinationa12 to which the solar tracker 1000 faces and on a solar term a40, arotation angle of the declination rotation shaft 300 or a correspondingsolar term a40 may be verified although the markings are indicated atany point of the power transfer path. Thus, various methods may beapplicable in addition to the example described in the foregoing.

For example, an additional rotation shaft may be provided formeasurement at one point at which power is transferred from the rightascension rotation actuator 200 to the declination rotation shaft 300,and a rotation plate having markings at an end thereof may be installed.When the right ascension rotation shaft 100 reciprocatingly rotates anda one-way rotation component is transferred to the declination rotationshaft 300 through the one-way clutch 450, the declination display device460 or the solar term display device 470 needs to be installed at onepoint of a power shaft to which a rectified rotation component istransferred through the one-way clutch 450.

Further, improper operation of the solar tracker 1000 may be readilyverified in the presence of a right ascension display device 480 for theright ascension rotation shaft 100. FIG. 15 also illustrates an exampleof the right ascension display device 480 applying a right ascensionmeasuring pointer 481 and a right ascension marking 482 to thedeclination rotation support 540 and the right ascension rotationsupport 530, respectively.

FIG. 18 is a flowchart illustrating an example four-step method ofoperating the solar tracker 1000 according to an embodiment of thepresent invention.

In a first step (S01), the method includes matching a direction of theright ascension rotation shaft 100 to the Earth's rotation axis a34.

In a second step (S02), the method includes matching an angle of thedeclination rotation shaft 300 to a declination a12 of the Sun a01.

In a third step (S03), the method includes tracking a diurnal motion ofthe Sun a01 by actuating the right ascension rotation shaft 100 throughthe right ascension rotation actuator 200.

In a fourth step (S04), the method includes tracking a change in ameridian altitude a23 of the Sun a01 occurring due to an annual motionby transferring a portion of driving power of the right ascensionrotation actuator 200 to the declination rotation shaft 300 through thedeclination actuation mechanism 400.

The following steps may be additionally included in the method asnecessary.

In a fifth step (505), when a motional displacement of the declinationrotation shaft 300 is less or greater than the Earth's rotational axialtilt a05, the method includes changing the motional displacement of thedeclination rotation shaft 300 by adjusting the declination actuationmechanism 400.

In a sixth step (506), when a motion cycle of the declination rotationshaft 300 is longer or shorter than a revolution cycle of the Earth a02,the method includes changing the motion cycle of the declinationrotation shaft 300 by adjusting the reduction ratio adjuster 440.

In a seventh step (507), when a difference between an angle of thedeclination rotation shaft 300 and a declination a12 of the Sun a01 islarge, the method includes releasing the coupling 430 and resetting theangle of the declination rotation shaft 300.

FIG. 19 is a flowchart illustrating an example seven-step method ofoperating the solar tracker 1000 in which the additional steps, forexample, the fifth step (S05), the sixth step (S06), and the seventhstep (S07), are all included.

Hereinafter, each step of the method of operating the solar tracker 1000will be described in detail. For an appropriate operation of the solartracker 1000, accurate installation needs to be performed in accordancewith the first step and the second step.

The method of operating the solar tracker 1000 includes the first step(S01) of adjusting and matching a direction of the right ascensionrotation shaft 100 to the Earth's rotation axis a34. A first task to beperformed to implement the solar tracker 1000 may include preparingrobust fundamentals on the ground, and installing the solar tracker 1000to match the right ascension rotation shaft 100 to the Earth's rotationaxis using measuring apparatuses such as a horizontal level measurerconfigured to determine a reference of an inclination of the ground, anangle measurer configured to measure an inclination or a tilt, adistance measurer configured to measure a distance, a compass configuredto measure a magnetic north, and a theodolite or a total stationconfigured to measure a true north. Here, simultaneously matching twoangles—an azimuth a21 on the horizontal plane a29 and an altitude a22facing the sky—is necessary. A method of matching the azimuth a21includes projecting the right ascension rotation shaft 100 to the groundto place the right ascension rotation shaft 100 on a plane through whicha meridian a24 passes and to make both ends face the south and thenorth, respectively. In the example of using the one pillar 520illustrated in (a) of FIG. 7, the matching of the direction may beperformed by suitably rotating the pillar 520. In the example of usingthe two pillars 520 a and 520 b illustrated in (b) of FIG. 7, thematching of the direction may be performed by adjusting a relativeposition of each pillar.

A method of matching the altitude a22 includes adjusting an angle formedbetween the right ascension rotation shaft 100 and the horizontal planea29 based on a latitude a32 of an installation location. For example, ina case of the northern hemisphere, an angle formed between the rightascension rotation shaft 100 and the ground with respect to a northpoint a26 is adjusted to be tilted by a latitude a32 of the installationlocation. In a case of the southern hemisphere, an angle formed betweenthe right ascension rotation shaft 100 and the ground with respect to asouth point a25 is adjusted to be tilted by a latitude a32 of theinstallation location. Thus, when the installation location is on theequator a37, the right ascension rotation shaft 100 is parallel with thehorizontal plane a29. When the installation location is in the NorthPole a35 or the South Pole a36, the right ascension rotation shaft 100is set up perpendicularly to the horizontal plane a29 as shown in thepillar 520. When the installation location is in Korea, the rightascension rotation shaft 100 is installed to be tilted at approximately37° from the north point a26, and tilted at approximately 143° from thesouth point a25 passing a zenith to the horizontal plane a29. In theexample of using the one pillar 520, an altitude a22 of the rightascension rotation shaft 100 may be adjusted by suitably tilting theright ascension rotation support 530 fixed to the pillar 520. In theexample of using the two pillars 520 a and 520 b, an altitude a22 of theright ascension rotation shaft 100 may be adjusted by adjusting a heightof the pillar 520 a or the pillar 520 b which has an adjustable length.

The method of operating the solar tracker 1000 includes the second step(S02) of matching an angle of the declination rotation shaft 300 to adeclination a12 of the Sun a01 based on a solar term a40. At an initialinstallation of the solar tracker 1000, the second step (S02) ofadjusting the declination rotation shaft 300 needs to be appropriatelyperformed in addition to the first step (S01). The second step (S02)includes adjusting an angle of the declination rotation shaft 100 basedon a distance between the equatorial plane a17 and the ecliptic a18based on a solar term a40, for example, a declination a12 of the Sun a01based on a season, and changing an angle of the light collector holder550 to allow the attached light collector 600 to face the Sun a01. Asdescribed with reference to Equation 4, a declination a12 of the Sun a01monotonically increases until the declination a12 reaches an angle ofthe Earth's rotational axial tilt a05 in the summer solstice a44 afterpassing through a point at which the declination a12 is 0 in the springequinox a41, for example, passing through the equatorial plane a17 ofthe celestial sphere a19. The declination a12 increases to a meridianaltitude a23 at a maximum angle in the summer solstice a44 and decreasesafterwards, and passes through the equatorial plane a17 of the celestialsphere a19 and stays in the southern hemisphere after the autumn equinoxa43. The meridian altitude a23 of the Sun a01 has a minimum angle in thewinter solstice a44. Since a change of season in the southern hemisphereof the Earth a02 occurs conversely in the northern hemisphere and areference point for measurement and a seasonal solar term a40 changes,the solar tracker 1000 needs to operate based on such a fact.

In an example of the solar tracker 1000 without the coupling 430, anangle of the declination rotation shaft 300 needs to be adjusted to havea suitable declination a12 based on a solar term a40 in conjunction withthe right ascension rotation shaft continuously rotating. Since thedeclination rotation shaft 300 performs only one cycle of a motion whilethe right ascension rotation shaft 100 rotates approximately 365 times,the right ascension rotation shaft 100 needs to greatly rotate for asmall movement of the declination rotation shaft 300 and thus, aninconvenience may occur. However, in an example of the solar tracker1000 including the coupling 430, a dependent relationship between theright ascension rotation shaft 100 and the declination rotation shaft300 may be immediately removed, and the declination rotation shaft 300may be independently adjusted. When the coupling 430 installed in apower transfer shaft of the declination actuation mechanism 400 isreleased, an angle of the declination rotation shaft 300 and the lightcollector holder 550 attached thereto may be unrestrictedly adjustedwithout affecting the right ascension rotation shaft 100.

In an example of the solar tracker 1000 including the declinationdisplay device 460, a declination a12 on the celestial sphere a19 towardwhich the light collector 600 faces may be readily verified through thedeclination marking 462 of the declination display device 460 without anadditional measuring apparatus. By referring to the declination marking462, the declination rotation shaft 300 may be adjusted. In an exampleof the solar tracker 1000 including the solar term display device 460, adeclination a12 of the Sun a01 based on a seasonal solar term a40 may beconverted and thus, an inconvenience in adjusting an angle of thedeclination rotation shaft 300 may be relieved. In the example of thesolar tracker 1000 including the solar term display device 460, an angleof the declination rotation shaft 300 is converted to a seasonal solarterm a40 and the solar term a40 is displayed. Thus, adjusting the angleof the declination rotation shaft 300 to a current solar term a40 mayonly be performed after reading the solar term marking 472 withoutperforming a comparison of an angle of the declination rotation shaft300 and a declination a12 of the Sun a01. That is, a time comparisonmethod may be more intuitive than an angle comparison method.

The first step (S01) and the second step (S02) described in theforegoing are prerequisites for the initial installation of the solartracker 1000. Hereinafter, the third step (S03) and the fourth step(S04) will be described in detail and theses steps may be prerequisitesfor a process of tracking the Sun a01 after the initial installation ofthe solar tracker 1000.

The method of operating the solar tracker 1000 includes the third step(S03) of tracking the diurnal motion of the Sun a01 by actuating theright ascension rotation shaft 100 through the right ascension rotationactuator 200. After completing the initial installation of the solartracker 1000 in accordance with the first step (S01) and the second step(S02), the solar tracker 1000 is activated to allow the light collector600 attached to the solar tracker 1000 to move along the diurnal motionof the Sun a01 occurring every day. A simplest method of tracking thediurnal motion may include operating the right ascension rotation shaft100 at a constant angular velocity of an approximately 15° per hour atwhich the Earth a02 rotates, starting from a certain angle in the eastat a certain time in the morning, in accordance with a predeterminedprogram, and suspending such an operation at a certain angle in the westin a certain time in the evening and returning to the east at night. Insuch a manual tracking method by the time-based program, the Sun a01 maybe precisely tracked without a significant error when data on a latitudea32 and a longitude a31 of a location at which the solar tracker 1000 isinstalled is correct and a direction of the right ascension rotationshaft 100 is accurately installed. In operating the time-based program,since a revolution orbit of the Earth a02 is not an exact circle, but anellipse, the equation of time of a maximum eight minutes, whichcorresponds to a tracking error of approximately 2.5° when converted toan angular velocity, may occur due to a difference in a revolution speedat a perihelion and at an aphelion. Thus, the program may more preciselyoperate by correcting the equation of time from a mean solar time basedon Kepler's laws. However, in such a manual tracking method based on theprogram, a real-time correction may be impossible when an error occursdue to an external factor such as a slip effect of an actuator. Toimprove the manual tracking method, a sensor-based active trackingmethod may be used to measure, in real time, a position of the Sun a01through an included sensor configured to sense the Sun a01 and actuatethe right ascension rotation shaft 100 based on the measured position ofthe Sun a01. In such an active tracking method, despite an externalissue such as a breakdown, the actuation may be enabled throughreal-time verification of an actual position of the Sun a01. However, anoperation may be temporarily suspended due to an influence of weather ora passing obstacle, and a speed may fluctuate without maintaining aconstant speed due to a vulnerability to vibration. Thus, the twomethods described in the foregoing may be used in combination. The solartracker 1000 may operate based on time using data on an observationpoint in accordance with the predetermined program and monitor a stateof tracking the Sun a01 using the sensor, and also correct an error inreal time in a case of a significant error.

The method of operating the solar tracker 1000 includes the fourth step(S04) of tracking a change in a meridian altitude a23 of the Sun a01based on a solar term a40 by transferring a portion of driving power ofthe right ascension rotation actuator 200 to the declination rotationshaft 300 through the declination actuation mechanism 400. The fourthstep (S04) is automatically generated from the third step (S03). In thethird step (S03), when the right ascension rotation shaft 100 rotatesalong a direction of the diurnal motion of the Sun a01, a rotation angleof the right ascension rotation shaft 100 is transferred to thedeclination rotation shaft 300 through the declination actuationmechanism 400 and the declination rotation shaft 300 reciprocatinglyrotates upwards and downwards along the annual motion of the Sun a01.The driving power is extracted from one point in a power transfer pathof the right ascension rotation actuator 200 and used to actuate thedeclination rotation shaft 300 through the declination actuationmechanism 400. Here, when the right ascension rotation shaft 100 doesnot continuously rotate in one direction, the one-way clutch 450 is usedto selectively transfer a one-way rotation component that tracks onlythe diurnal motion of the Sun a01. The declination actuation mechanism400 is designed to match an amount of rotation accumulated for one yearduring which the right ascension rotation shaft 100 tracks the diurnalmotion of the Sun a01 to a cycle of the reciprocating up and downrotational motion of the declination rotation shaft 300. Here, thedesigning may be readily performed by adjusting a reduction gear ratioat which the output shaft of the declination reducer 410 of thedeclination actuation mechanism 400 makes one rotation per year. Forexample, the crank 421 is installed in the output shaft of thedeclination reducer 410, and the rocker 422 that rotates upwards anddownwards along the annual motion of the Sun a01 is installed in thedeclination rotation shaft 300 to form the four-bar linkage. Thus, whenthe crank 421 makes one rotation per year, the declination rotationshaft 300 fixed with the rocker 422 reciprocatingly rotates upwards anddownwards on one year cycle. Here, when relative lengths of the crank421, the connecting rod 423, and the rocker 422, and respectivepositions of each connection joint are adjustable, changing a motionalrange of the four-bar linkage and adjusting the declination rotationshaft 300 to have an angle of the Earth's rotational axial tilt a05 inan upward and a downward side, respectively, may be readily performed.The method of operating the solar tracker 1000 may be performed onlywith the four steps including the first step (S01) through the fourthstep (S04). However, for maintenance, the additional steps, the fifthstep (S05), the sixth step (S06), or the seventh step (S07) may be addedto the method.

When a motional displacement of the declination rotation shaft 300 isgreater or less than the Earth's rotational axial tilt a05, the methodof operating the solar tracker 1000 may include the fifth step (S05) ofchanging the motional displacement of the declination rotation shaft 300by adjusting the declination actuation mechanism 400. When the motionaldisplacement of the declination rotation shaft 300 rotating upwards anddownwards on one year cycle is less or greater than the Earth'srotational axial tilt a05, an error in tracking the Sun a01 mayincrease. The motional displacement of the declination rotation shaft300 is a value determined based on a mechanical configuration of thedeclination actuation mechanism 400, and needs to be accurately designedto have a suitable range. In an example of the declination actuationmechanism 400, the motional displacement and a sectional speed may beadjusted by adjusting a position of a joint of the crank 421, the rocker422, or the connecting rod 423, and a link length. In addition to themotional displacement of the declination rotation shaft 300, variousoperation characteristics including a motional trajectory and asectional speed may be adjusted by adjusting the link length and theposition of each connection joint. However, the motional displacement ofthe declination rotation shaft 300 may not change depending on aninstallation location or a surrounding environment and thus, thedeclination rotation shaft 300 may operate identically anywhere on theEarth a02 and a situation in which the motional displacement of thedeclination rotation shaft 300 needs to be adjusted may not occurfrequently.

When a motion cycle of the declination rotation shaft 300 is longer orshorter than a cycle of revolution of the Earth a02, the method ofoperating the solar tracker 1000 may include the sixth step (S06) ofchanging the motion cycle of the declination rotation shaft 300 byadjusting the reduction ratio adjuster 440. In a long-term operation ofthe solar tracker 1000, the motion cycle of the declination rotationshaft 300 may become gradually faster or slower than a cycle of theannual motion of the Sun a01. Here, a rotation range of the rightascension rotation shaft 100 tracking the diurnal motion per day may beadjusted based on an environmental condition such as a surroundinggeographic feature of an installation location, and a reduction gearratio of the declination actuation mechanism 400 may need to be adjustedaccordingly. For example, in an open location such as a beach, the rightascension rotation shaft 100 rotates up to a maximum 180° per day. In amountainous region around which numerous obstacles are present, asunrise time is moved forward and a sunset time is moved backward andthus, an amount of daily rotation may be reduced. Despite an amount ofrotation of the right ascension rotation shaft 100 varying depending ona region or a location, a rotation angle at which the declinationrotation shaft 300 moves a day to track the annual motion of the Sun a01is invariant as described with reference to Equation 4. Thus, adjustingthe reduction gear ratio of the declination actuation mechanism 400 isrequired based on an operation range of the right ascension rotationshaft 100 for which an environment of the installation location isconsidered. In an operation of the solar tracker 1000, a lack of thereduction gear ratio of the declination actuation mechanism 400 may leadto a shortening cycle of the reciprocating up and down rotational motionof the declination rotation shaft 300 compared to an actual cycle ofrevolution of the Earth a02. Thus, increasing the reduction gear ratiomay be necessary. Conversely, a large reduction gear ratio may lead to aprolonged motion cycle of the declination rotation shaft 300 compared tothe actual cycle of revolution of the Earth a02. Thus, decreasing thereduction gear ratio may be necessary. In an example of the solartracker 1000 including the declination display device 460 or the solarterm display device 470, verifying an error in the motion cycle may bereadily performed by referring to the declination display device 460 orthe solar term display device 470. When the error is verified to occurafter periodically verifying the motion cycle of the declinationrotation shaft 300, the reduction gear ratio of the declinationactuation mechanism 400 may need to be suitably adjusted to increase ordecrease the reduction gear ratio to remove the error. In a case of afixed reduction gear ratio of the declination actuation mechanism 400,changing the motion cycle of the declination rotation shaft 300 may beinconvenient and thus, attaching the reduction ratio adjuster 440 isrecommended herein.

When a difference between an angle of the declination rotation shaft 300and a declination a12 of the Sun a01 is large, the method of operatingthe solar tracker 1000 may include the seventh step (S07) of releasingthe coupling 430 and resetting an angle of the declination rotationshaft 300. In a long-term operation of the solar tracker 1000, an errormay occur in relation to the motional displacement or the motion cycleof the declination rotation shaft 300. In such a case, an error that maypotentially occur may be reduced using the methods provided in the fifthstep (S05) and the sixth step (S06). However, since an alreadyaccumulated error remains, an additional step to remove the error may benecessary. To remove an error accumulated while the declination rotationshaft 300 tracks a declination a12 of the Sun a01, a method similar tothe method provided in the second step (S02) may be applied. The methodmay include releasing the coupling 430, independently rotating thedeclination rotation shaft 300 to remove the accumulated error, andconnecting the coupling 430 again to allow the declination rotationshaft 300 to interwork with the right ascension rotation shaft 100.

1. A solar tracker 1000, comprising: a right ascension rotation shaft100 installed in parallel with the Earth's rotation axis a34 andconfigured to track a change in a right ascension a11 occurring due to adiurnal motion of the Sun a01; a right ascension rotation actuator 200configured to actuate the right ascension rotation shaft 100; adeclination rotation shaft 300 perpendicular to the right ascensionrotation shaft 100 and configured to reciprocatingly rotate on a fourseason cycle to track a change in a declination a12 occurring due to anannual motion of the Sun a01; and a declination actuation mechanism 400configured to transfer a portion of rotational power generated when theright ascension rotation actuator 200 actuates the right ascensionrotation shaft 100 to the declination rotation shaft 300 to allow thedeclination rotation shaft 300 to reciprocatingly rotate upwards anddownwards, and comprising a one-way clutch 450 installed at one point ina power transfer path from the right ascension rotation actuator 200 tothe declination rotation shaft 300 and configured to select and transfera one-way rotation component of the rotational power to be transferredto the declination rotation shaft
 300. 2. The solar tracker 1000 ofclaim 1, comprising: a reduction ratio adjuster 440 installed at onepoint in the power transfer path from the right ascension rotationactuator 200 to the declination rotation shaft 300 and configured toincrease or decrease a rotation ratio to be transferred.
 3. The solartracker 1000 of claim 1, comprising: a coupling 430 installed at onepoint in the power transfer path from the right ascension rotationactuator 200 to the declination rotation shaft 300 and configured toconnect or block the rotational power to be transferred.
 4. The solartracker 1000 of claim 1, wherein the declination actuation mechanism 400comprises: a declination reducer 410 configured to receive driving powerof the right ascension rotation actuator 200, convert a rotation ratio,and output the converted rotation ratio; a crank 421 attached to anoutput shaft of the declination reducer 410; a rocker 422 fixed to thedeclination rotation shaft 300 and reciprocatingly rotating upwards anddownwards at the Earth's rotational axial tilt a05 based on the changein the declination a12 occurring due to the annual motion of the Suna01; and a connecting rod 423 connecting one end of the crank 421 to oneend of the rocker 422 to form a four-bar linkage 420, and configured toconvert a rotational motion of the crank 421 to the reciprocating up anddown rotational motion of the rocker
 422. 5. The solar tracker 1000 ofclaim 4, wherein the crank 421, the rocker 422, or the connecting rod423 comprises an adjuster 424 configured to adjust a location of a jointor a link length to change a motional displacement and a sectional speedof the reciprocating up and down rotational motion of the declinationrotation shaft
 300. 6. The solar tracker 1000 of claim 1, comprising: adeclination display device 460 configured to convert an amount ofrotation of the declination rotation shaft 300 to an angle and displaythe angle; or a solar term display device 470 configured to convert theamount of rotation to a solar term a40 of a year and display the solarterm a40.
 7. A method of operating a solar tracker 1000, comprising: afirst operation S01 to match a direction of a right ascension rotationshaft 100 to the Earth's rotation axis a34; a second operation S02 tomatch an angle of a declination rotation shaft 300 to a declination a12of the Sun a01; a third operation S03 to track a diurnal motion of theSun a01 by actuating the right ascension rotation shaft 100 by a rightascension rotation actuator 200; and a fourth operation S04 to track, bythe declination rotation shaft 300, a change in a meridian altitude a23of the Sun a01 occurring due to an annual motion, by allowing adeclination actuation mechanism 400 to selectively extract a one-wayrotation component and allow the declination rotation shaft 300 toreciprocatingly rotate on a four season cycle when the declinationactuation mechanism 400 transfers a portion of driving power of theright ascension rotation actuator 200 to the declination rotation shaft300.
 8. The method of claim 7, comprising any one of: a fifth operationS05 to change a motional displacement of the declination rotation shaft300 by adjusting the declination actuation mechanism 400 in response tothe motional displacement of the declination rotation shaft 300 beingless or greater than the Earth's rotational axial tilt a05; a sixthoperation S06 to change a motion cycle of the declination rotation shaft300 by adjusting a reduction ratio adjuster 440 in response to themotion cycle of the declination rotation shaft 300 being longer orshorter than a cycle of revolution of the Earth a02; and a seventhoperation S07 to release a coupling 430 and reset an angle of thedeclination rotation shaft 300 in response to a large difference betweenthe angle of the declination rotation shaft 300 and the declination a12of the Sun a01.
 9. The method of claim 7, wherein an angle at which thedeclination rotation shaft 300 reciprocatingly rotates upwards anddownwards in the fourth operation S04 corresponds to the Earth'srotational axial tilt a05 in each of an upward direction and a downwarddirection.
 10. The solar tracker 1000 of claim 1, comprising: a balanceweight 560 configured to adjust a weight and an attached location of aload to allow a centroid of the load applied to each rotation shaft tobe positioned in each rotation shaft by changing the centroid of theload, in order to prevent a rotation by a self weight and minimize anamount of rotational power required for actuating a rotation shaftthrough a balance of the load applied to the right ascension rotationshaft 100 or the declination rotation shaft 300.